Semiconductor processing methods and integrated circuitry

ABSTRACT

In aspect, the invention includes a semiconductor processing method comprising: a) forming an electrically insulative layer over a substrate; b) forming an opening within the electrically insulative layer, the opening having a periphery defined at least in part by a bottom surface and a sidewall surface; c) forming a first layer comprising TiN within the opening, the first layer being over the bottom surface and along the sidewall surface; d) forming a second layer comprising elemental Ti over the electrically insulative layer but substantially not within the opening, the second layer having a thickness of less than 50 Å along the sidewall surface and over the bottom surface; and e) forming an aluminum-comprising layer within the opening and over the second layer. In another aspect, the invention includes a semiconductor processing method comprising: a) forming a first aluminum-comprising layer over an electrically insulative layer; b) forming a first titanium-comprising layer over the first aluminum-comprising layer; c) forming a second titanium-comprising layer over the first titanium-comprising layer, one of the first and second titanium-comprising layers comprising elemental Ti and the other of the first and second titanium-comprising layers comprising TiN; and d) forming a second aluminum-comprising layer over the second titanium-comprising layer.

TECHNICAL FIELD

The invention pertains to semiconductor processing methods andintegrated circuitry. The invention has particular application tosemiconductor processing methods of depositing aluminum, and tointegrated circuitry comprising aluminum.

BACKGROUND OF THE INVENTION

It is frequently desired to for aluminum within high aspect ratiocontact openings during semiconductor fabrication. The contact openingsex tend through, for example, an insulative material. The aluminumfunctions as a conductive metal contact within the contact openings. Thealuminum also generally extends beyond the contact openings to formwiring interconnect layers which electrically connect the metal contactswithin the contact openings to other circuitry. The aluminum extendingbeyond the contact openings can lie over the insulative material throughwhich the contact openings are formed. Unfortunately, if aluminum isdeposited over a material there will frequently be stress-induced voidsdeveloped along edges of the deposited aluminum. It would be desirableto develop methods of forming aluminum wherein stress-induced voidformation is substantially avoided.

A recently developed method of depositing aluminum is a so-called coldwall chemical vapor deposition (CVD) process, which can use, forexample, dimethyl aluminum hydride (DMAH) as an aluminum precursor. Thechemical vapor deposited aluminum nucleates better to titanium nitride(TiN) than to many other materials. Accordingly, a TiN layer isfrequently provided prior to chemical vapor deposition of aluminum.

SUMMARY OF THE INVENTION

In one aspect, the invention encompasses a semiconductor processingmethod wherein an electrically insulative layer is formed over asubstrate. An opening is formed within the electrically insulativelayer. The opening has a periphery defined at least in part by a bottomsurface and a sidewall surface. A first layer comprising TiN is formedwithin the opening. The first layer is over the bottom surface and alongthe sidewall surface. A second layer comprising elemental Ti is formedover the electrically insulative layer. The second layer issubstantially not within the opening. The second layer has a thicknessof less than 200 Angstroms along the sidewall surface and over thebottom surface. An aluminum-comprising layer is formed within theopening and over the second layer.

In another aspect, the invention encompasses a semiconductor processingmethod wherein an electrically insulative layer is formed over asubstrate. An opening is formed within the electrically insulativelayer. The opening has a periphery that is defined at least in part by abottom surface and a sidewall surface. A first layer comprising TiN isformed within the opening. The first layer formed is over the bottomsurface and along the sidewall surface. A second layer comprisingelemental Ti is formed over the electrically insulative layer and overthe bottom of the opening. The second layer is substantially not along apredominate portion of the sidewall surface. The second layer has athickness of less than 200 Angstroms along a predominate portion of thesidewall surface and a thickness of at least about 200 Angstroms overthe bottom surface. An aluminum-comprising layer is formed within theopening and over the second layer.

In yet another aspect, the invention encompasses a semiconductorprocessing method wherein an electrically insulative layer is formedover a silicon-comprising substrate. An opening is formed within theelectrically insulative layer. The opening extends to the substrate andhas a periphery defined in part by a bottom surface. A titanium-silicidelayer is formed at the bottom surface. A first layer comprising TiN isformed within the opening and over the titanium silicide. A second layercomprising elemental Ti is formed over the first layer. A firstaluminum-comprising layer is formed within the opening and over thesecond layer. The aluminum-comprising layer contacts the second layer atthe bottom surface. A third layer is formed over the firstaluminum-comprising layer. The third layer comprises one of elemental Tior TiN. A second aluminum-comprising layer is formed over the thirdlayer.

In other aspects, the invention encompasses structures formed by theabove-described methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a fragmentary, diagrammatic, cross-sectional view of asemiconductor wafer fragment at a preliminary processing step of amethod of the present invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown in FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that of FIG. 2, in accordance with a first embodimentmethod of the present invention.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown in FIG. 2, in accordance with a secondembodiment method of the present invention.

FIG. 5 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown in FIG. 4.

FIG. 6 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown in FIG. 2, in accordance with a thirdembodiment method of the present invention.

FIG. 7 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

A first embodiment of the invention is described with reference to FIGS.1-3. Referring to FIG. 1, a semiconductor wafer fragment 10 isillustrated at a preliminary processing step of a method of the presentinvention. Wafer fragment 10 comprises a substrate 12 and anelectrically insulative layer 14 overlying substrate 12. Substrate 12can comprise, for example, a monocrystalline silicon wafer lightly dopedwith a conductivity-enhancing dopant. To aid in interpretation of theclaims that follow, the term “semiconductive substrate” is defined tomean any construction comprising semiconductive material, including, butnot limited to, bulk semiconductive materials such as a semiconductivewafer (either alone or in assemblies comprising other materialsthereon), and semiconductive material layers (either alone or inassemblies comprising other materials). The term “substrate” refers toany supporting structure, including, but not limited to, thesemiconductive substrates described above.

A node location 16 is defined within substrate 12. Node location 16 willultimately comprise an electrically conductive node. For instance, nodelocation 16 can ultimately comprise a diffusion region conductivelydoped with a conductivity-enhancing dopant. If node location 16 is toultimately comprise such diffusion region, the conductivity-enhancingdopant can be implanted into node location 16 prior to formation ofinsulative layer 14. Alternatively, the conductivity-enhancing dopantcan be implanted within node location 16 at processing steps subsequentto formation of layer 14, such as after formation of an opening 20(described with reference to FIG. 2) extending through insulative layer14.

Insulative layer 14 can comprise, for example, borophosphosilicate glass(BPSG), and can be formed by conventional methods.

Referring to FIG. 2, a contact opening 20 is formed through insulativelayer 14 and to node location 16. Opening 20 can be formed byconventional methods. Opening 20 has a periphery defined at least inpart by a bottom surface 22 and a sidewall surface 24. Typically,opening 20 is defined by a circular horizontal cross-sectional shapesuch that a single sidewall surface 24 completely defines the entirelateral periphery of opening 20. This typical configuration is shown inthe vertical cross-sectional view of FIG. 2 wherein a common sidewallsurface 24 is shown at opposing lateral sides of opening 20. Inalternative configurations, the side periphery of opening 20 cancomprise sharp corners, such as, for example, in a polygonalconfiguration. In such alternative embodiments, the lateral periphery ofopening 20 would be defined by a number of sidewall surfaces.

A layer 26 is formed over insulative layer 14 and at bottom surface 22of opening 20. Layer 26 preferably comprises elemental titanium, and canbe formed by, for example, chemical vapor deposition of elementaltitanium under the conditions of an RF plasma at 650° C. and 5 Torr withTiCl₄ and H₂. An elemental titanium layer 26 typically has a thicknessof less than 75 Angstroms at sidewall surfaces 24 of opening 20.

A portion of layer 26 at bottom surface 22 can be subsequently processedto convert the layer to titanium silicide. For example, in embodimentsin which substrate 12 comprises silicon, layer 26 at bottom surface 22can be heated to a temperature of greater than 600° C. to convert theelemental titanium in contact with silicon 12 to titanium silicide.

A titanium-comprising layer 28 is formed over layer 26 and withinopening 20. Layer 28 preferably comprises titanium nitride and can beformed by, for example, chemical vapor deposition or sputter deposition.Layer 28 is formed over insulative layer 14, and over bottom surface 22of opening 20. Further, layer 28 adheres to insulative material 14 tocover sidewall surface 24 of opening 20.

Referring to FIG. 3, a conductive layer 30 is formed within opening 20(shown in FIG. 2), and over insulative layer 14. Conductive layer 30preferably comprises aluminum. Conductive layer 30 can be formed, forexample, by chemical vapor deposition utilizing DMAH, or, lesspreferably, by sputter deposition. An aluminum-comprising layer 30 ispreferably provided to a thickness of at least about half the width ofopening 20 to completely fill opening 20. The thickness ofaluminum-comprising layer 30 is preferably not more than about 80%greater than half the width of opening 20, as thicker layers are morelikely to suffer from surface roughness. If layer 30 comprises aluminum,it can be formed by, for example, chemical vapor deposition or sputterdeposition. An aluminum layer 30 is preferably formed to a thickness ofless than or equal to about 2000 Angstroms. Thicker layers of aluminumare found to have rougher outer surfaces than thinner layers, and it hasbeen determined that aluminum layers greater than about 2000 Angstromsthick have unacceptably rough outer surfaces for utilization in furthersemiconductor processing steps.

After formation of aluminum layer 30, a first overlyingtitanium-comprising layer 32 is formed over layer 30, and a secondoverlying titanium-comprising layer 34 is formed over firsttitanium-comprising layer 32. Preferably, one of layers 32 and 34comprises elemental Ti, and the other of layers 32 and 34 comprises TiN.Layers 32 and 34 can be formed by conventional methods, such as, forexample, chemical vapor deposition or sputter deposition.

A second conductive layer 36 is formed over layers 32 and 34. Conductivelayer 36 preferably comprises a material in common with conductive layer30. For example, layers 30 and 36 preferably both comprise aluminum.

Layers 30, 32, 34 and 36 together comprise a conductive interconnect 38.(The term “conductive interconnect” can also encompass subsets of layers30, 32, 34 and 36, such as, for example, layers 32/34 or layers32/34/36.) Layers 32 and 30 within conductive interconnect 38 reducestress induced voiding in lines made by etching this stack. One oflayers 32 and 34 can be eliminated and some stress reduction will stilloccur. Preferably, if one of layers 32 and 34 is eliminated, theremaining layer will comprise elemental Ti. Elemental Ti has been foundto better reduce stress in an aluminum wiring layer than TiN. Anadvantage in incorporating a TiN layer into interconnect layer 38 isthat deposited aluminum nucleates better to TiN than to elemental Ti.The most preferred method of construction of interconnect 38 comprisesforming a lower layer 32 comprising elemental Ti and forming an upperlayer 34 comprising TiN. The resulting interconnect 38 then has thestress reducing advantages of elemental Ti and the aluminum nucleatingproperties of TiN.

A second embodiment of the invention is discussed with reference toFIGS. 4 and 5. In describing the second embodiment, similar numbering tothat utilized above in describing the first embodiment of FIGS. 1-3 willbe used, with differences indicated by the suffix “a” or by differentnumerals.

Referring to FIG. 4, a semiconductor wafer fragment 10 a is illustrated.Wafer fragment 10 a is shown at a processing step subsequent to that ofwafer fragment 10 of FIG. 2. Accordingly, wafer fragment 10 a comprisesan opening 20 a formed through an insulative layer 14 a to a substrate12 a. Wafer fragment 10 a further comprises a first layer 26 a and asecond layer 28 a formed within opening 20 a, with layer 26 a being at abottom surface 22 a of opening 20 a, and layer 28 a covering sidewallsurface 24 a and bottom surface 22 a of opening 20 a.

A layer 50 is formed over insulative layer 14 a, and over bottom surface22 a of opening 20 a. Layer 50 preferably comprises elemental titanium,and can be formed by, for example, chemical vapor deposition under theconditions of an RF plasma at 500° C. and 5 Torr with TiCl₄ and H₂.Alternatively, TiI₄ can be used in place of TiCl₄ and the temperaturecan be lowered to below 500° C. Layer 50 is formed over a bottom ofopening 20 a to a thickness of at least about 100 Å. Layer 50 issubstantially not formed along a predominant portion of sidewall surface24 a. For purposes of interpreting this disclosure and the claims thatfollow, a layer is defined as being substantially not formed along asurface if a thickness of the layer is less than 75 Angstroms thick overthe surface. The only portion of sidewall surface 24 a that layer 50 issubstantially formed along is a small portion proximate bottom surface22 a of opening 20 a.

A conductive layer 30 a is formed over layer 50 and within opening 20 a.Conductive layer 30 a preferably comprises aluminum. Layer 50 preferablycomprises elemental titanium to reduce a stress of aluminum-comprisinglayer 30 a on bottom surface 22 a of opening 20 a, as well as on anupper surface of insulative layer 14 a.

Referring to FIG. 5, one or more titanium-comprising layers 32 a and 34a are preferably formed over conductive layer 30 a. Subsequently, asecond conductive layer 36 a is formed over titanium-comprising layers32 a and 34 a. Layers 30 a, 32 a, 34 a and 36 a form a conductiveinterconnect 38 a analogous to the interconnect 38 discussed above withreference to FIG. 3.

A third embodiment of the invention is discussed with reference to FIGS.6 and 7. In describing the third embodiment, similar numbering to thatutilized above in describing the embodiments of FIGS. 1-5 will be used,with differences indicated by the suffix “b” or by different numerals.

Referring to FIG. 6, a semiconductor wafer fragment 10 b is illustrated.Wafer fragment 10 b is shown at a processing step subsequent to that ofwafer fragment 10 of FIG. 2. Accordingly, wafer fragment 10 b comprisesan opening 20 b formed through an insulative layer 14 b to a substrate12 b. Opening 20 b comprises a sidewall surface 24 b and a bottomsurface 22 b.

A layer 50 b, preferably comprising elemental titanium, is formed overinsulative layer 14 b. Layer 50 is preferably about 100 Angstroms thickover layer 14 b. Layer 50 b and can be formed by, for example, chemicalvapor deposition utilizing an RF plasma at 500° C. and 5 Torr with TiCl₄and H₂.

The process conditions are preferably optimized such that layer 50 b issubstantially not formed within opening 20 b. Specifically, layer 50 bis substantially not formed over bottom surface 22 b or along sidewallsurface 24 b.

A conductive layer 30 b is formed over layer 50 and within opening 20 a.Conductive layer 30 b preferably comprises aluminum. Layer 50 bpreferably comprises elemental titanium to reduce a stress ofaluminum-comprising layer 30 b on an upper surface of insulative layer14 b. An advantage of keeping an elemental titanium layer 50 b fromforming within opening 20 b is to maintain high conductivity of analuminum layer 30 b within opening 20 b. If aluminum layer 30 b contactselemental titanium layer 50 b, an alloy will form at point of contact.Such alloy will have a higher resistance than the aluminum of layer 30b. If the alloy is formed in opening 20 b, the alloy will decrease aconductivity within the opening relative to the conductivity that wouldexist without the alloy. The amount of alloy formed depends on thethickness of the elemental titanium layer. Thus, it is advantageous tominimize the amount of an elemental titanium layer 50 b formed withinopening 20 b.

As discussed above, there is an advantage of decreased stress in havingaluminum formed against elemental titanium. However, there are someapplications in which stress induced by an aluminum layer is primarilyproblematic over an insulative layer, and not within an openingextending through an insulative layer. In such applications, the thirdembodiment process of the present invention is particularly beneficial.The third embodiment process forms an elemental-titanium-comprisingstress reduction layer 50 b over insulative layer 14 b, without formingthe elemental-titanium-comprising layer in a contact opening where it isunneeded and unwanted.

Referring to FIG. 7, one or more titanium-comprising layers 32 b and 34b are preferably formed over conductive layer 30 b. Subsequently, asecond conductive layer 36 b is formed over titanium-comprising layers32 b and 34 b. Layers 32 b, 34 b and 36 b preferably comprise the samepreferable constructions discussed above with reference to layers 32, 34and 36.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A semiconductor processing method comprising:forming an electrically insulative layer over a substrate; forming anopening within the electrically insulative layer, the opening having aperiphery defined at least in part by a bottom surface and a sidewallsurface; forming a first layer comprising TiN within the opening, thefirst layer being over the bottom surface and along the sidewallsurface; forming a second layer comprising elemental Ti over theelectrically insulative layer and over the bottom of the opening, thesecond layer substantially not being along a predominate portion of thesidewall surface, the second layer having a thickness of less than 75 Åalong a predominate portion of the sidewall surface and a thickness ofat least about 100 Å over the bottom surface; and forming analuminum-comprising layer within the opening and over the second layer.2. The method of claim 1 wherein the forming the aluminum-comprisinglayer comprises chemical vapor deposition of aluminum.
 3. The method ofclaim 1 wherein the aluminum-comprising layer contacts the first layeralong the sidewall surface and contacts the second layer over the bottomsurface.
 4. The method of claim 1 wherein the substrate comprisessilicon, the method further comprising forming a layer comprisingtitanium-silicide at the bottom surface and beneath the first layer.